Boreholes for hydrocarbon (oil and gas) production, as well as for other purposes, are usually drilled with a drill string that includes a tubular member (also referred to as a drill pipe) having a drilling assembly which includes a drill bit attached to the bottom end thereof. The drill bit is rotated to shear or disintegrate material of the rock formation to drill the wellbore. The drill string often includes tools or other devices that are in operation located downhole and therefore require remote activation and deactivation during drilling operations. Such tools and devices include, for example, reamers, stabilizers or force application members used for steering the drill bit.
Electro-mechanical control systems, for example, are often unreliable in such drilling environments. Remote control of downhole tool activation by agency of fluid pressure in the drill string often allows only a limited number of activation/deactivation cycles, after which the control system is to be reset, while reduction in effective drill string diameter result in some systems. Some reamer activation apparatuses, for example, make use of a ball-drop mechanism that permits a single activation cycle, after which a reset of the control system is required.
Using the drilling fluid (e.g., mud cycled down the drill string and back up a borehole annulus) as a deployment mechanism can introduce a risk of inadvertent tool activation or deactivation.